The present invention relates to a method and composition for preventing the deposition of pitch and other contaminants in the press section of a pulp and paper process, and particularly in a pulp and paper process that uses resinous mechanical pulps, either alone or in combination with recycled pulps.
Paper machines that make paper from resinous thermomechanical pulps have historically suffered from operational problems in the press section of the paper process. In particular, resinous materials or pitch can become trapped within the felt structure and can deposit on the surface of press felts, rolls, and uhle boxes, thereby hindering the effective removal of water from the paper web as it is being produced. As a result, these deposits cause reduced operational efficiency and reduce the quality of the paper being produced.
Heretofore, paper mill operators have attempted to deal with the problem of pitch deposition by applying surfactant-based cleaners, solvents, or mixtures thereof to the press section. The surfactant-based cleaners and solvents are either fed continuously while the paper machine is in operation and making paper (continuous cleaning) or when the paper machine is down and not making paper (batch cleaning) to remove pitch from the press section.
One particular class of surfactants that has traditionally been used to remove pitch deposits from felts using both continuous and batch cleaning processes are the alkyl phenol ethoxylates, e.g., the nonylphenol alkoxylates. U.S. Pat. Nos. 5,167,767; 5,520,781 and 5,575,893 describe the use of ethoxylated phenols such as nonylphenol ethoxylates for use as felt conditioners. Although these surfactants are commonly used, the federal government has begun to closely regulate the alkyl phenol ethoxylates due to concerns about their biodegradation and their possible estrogenic effects on aquatic life. In particular, the federal government has listed certain nonylphenol ethoxylates and related compounds and derivatives (e.g. nonylphenol based phosphate esters, octyl phenols, dinonyl phenols, dodecyl phenols and related alkylphenol based compounds) as SARA Toxic Release Chemicals and requires extensive reporting and tracking of many of these compounds.
The solvents that are used to remove pitch from the press section can also have undesirable environmental effects. For example, large quantities of high flash point solvents such as kerosene are presently used to remove pitch deposits. However, the use of large amounts of kerosene and other high flash point solvents is undesirable due to the potential adverse effects it can have on workers and the environment. Furthermore, paper mills are expected to reduce the use of solvents that contain volatile organic compounds (VOC""s) because the vapors from these solvents react in the atmosphere to create smog and other adverse atmospheric conditions.
In addition to environmental problems, most surfactant-based cleaners and solvents typically are not effective enough to prevent the need for downtime during operation of the paper mill. Although many prior art products extend the time between downtime periods or batch cleanings, these products generally do not eliminate the need for downtime. As is readily understood by those skilled in the art, it is advantageous for mills to operate with limited downtime. In particular, the felts in the pressing section can typically be used for between four and eight weeks before they are mechanically worn out and need to be replaced. Therefore, if a mill can run for four to eight weeks without downtime using a continuous cleaning process, it is economically advantageous.
The problem of pitch deposition on press section equipment has been further complicated by recent changes in the operation of paper mills. For example, the mill operators have begun to reuse water produced during operation of the paper mill to reduce fresh water consumption. Thus, contaminants that used to be eliminated from the mill now become more concentrated in the press section and show a greater tendency to deposit on the press section equipment.
Another recent change that makes eliminating the pitch deposition on press section equipment even more difficult is the recent trend towards recycling pulp. Recycled pulp typically includes high levels of contaminants such as inks and adhesives and these contaminants can also become mechanically trapped within the felt structure. Therefore, compositions for removing pitch generally must be able to remove the inks and adhesives that are trapped within the felt structure.
Therefore, there is a need in the art to produce a cleaning composition that can effectively remove pitch from felts and other pressing equipment in a continuous cleaning process without requiring downtime and batch cleaning. Furthermore, there is a need to produce a cleaning composition that is environmentally safe that effectively removes inks, adhesives, and other contaminants from pressing equipment.
The present invention provides a continuous method and composition for preventing the deposition of contaminants from resinous pulp and/or recycled pulp in the felt press section of a pulp and paper process. The present invention is highly effective in breaking down contaminants from resinous pulps and recycled pulps that are detrimental to press section and papermaking operations and that block felt surfaces. The method and composition of the invention eliminates the need for batch or downtime cleaning and allows the press section to operate with good efficiency to produce paper having good quality. The present method and composition has also been shown to be more effective than environmentally undesirable nonylphenol containing formulations. Furthermore, the present invention accomplishes effective cleaning using a low concentration of solvent-type materials.
The present invention provides a composition that includes a cleaning solvent comprising a blend of aromatic hydrocarbons containing between nine and eleven carbon atoms and a surfactant comprising an alcohol ethoxylate. The combination of the cleaning solvent and the alcohol ethoxylate, and particularly a branched or secondary alcohol ethoxylate, produces synergistic results in removing pitch and is useful in removing other contaminants from press machinery including ink, sizing agents, coatings, waxes and stickies. The composition is also substantially free of alkyl phenols, alkylphenol ethoxylates, naphthalene and other environmentally undesirable compounds. In addition, the composition of the invention provides effective cleaning while using a minimal amount of VOC""s.
In accordance with the invention, the composition for inhibiting the deposition of pitch and other deposits on pulp and paper machinery includes a cleaning solvent comprising a blend of aromatic hydrocarbons containing between nine and eleven carbon atoms and preferably having a flash point of greater than 140xc2x0 F., and an alcohol ethoxylate, preferably a branched or secondary alcohol ethoxylate, and more preferably a tridecyl alcohol ethoxylate. Preferably, the solvent of the composition is substantially free of naphthalene and the surfactant of the composition is substantially free of alkyl phenols and alkylphenol ethoxylates such as nonylphenol ethoxylates. The surfactant preferably includes between 6 and 16 moles ethylene oxide, more preferably between 8 and 10 moles ethylene oxide, per mole of alcohol. The mass ratio of cleaning solvent to alcohol ethoxylate in the present composition is preferably from about 1:10 to about 10:1, more preferably from about 1:3 to about 3:1. In addition to the cleaning solvent and the alcohol ethoxylate, the present composition can also include formulation solvents, water, additional surfactants, buffers and other additives.
The present invention further includes a continuous method for inhibiting the deposition of contaminants from resinous pulps and recycled pulps on machinery in a pulp pressing process. According to the present method, an advancing paper stock material is contacted with an advancing pressing felt to remove moisture from the paper stock material. After the advancing pressing felt contacts the paper stock material, a deposition-inhibiting effective amount of the cleaning composition described above is applied to the advancing felt, preferably by spraying, to loosen pitch and other deposited contaminants from the felt. The loosened contaminants are then removed from the advancing pressing felt and the advancing pressing felt is again contacted with paper stock material to remove moisture from the paper stock material. The present method operates continuously to reduce or eliminate the deposition of pitch and other contaminants thereby allowing the press section to operate without the need for downtime during the four to eight week life span of the felts.
These and other features and advantages of the present invention will become more readily apparent to those skilled in the art upon consideration of the following detailed description and accompanying drawings, which describe both the preferred and alternative embodiments of the present invention.